The self-assembly of metal nanoparticles driven by interactions of surface-anchored ligands such as DNA, multivalent thiolates, and proteins results in 1-, 2- and 3-dimensional nanoparticle superstructures. Such superstructures display emergent fundamental optical properties. Applications in sensing, plasmonics and biology arise from ensemble properties absent in discrete metal nanoparticles.
In the case of the widely studied gold nanoparticle assembly, the assembly is almost always mediated by thiol-anchored ligands. This results in largely static and stable assemblies, due to the comparatively strong Au—S bond precluding dynamic events. Any dynamic aspects of the assembly arise from plasticity within the ligand. However, new gold nanoparticle assemblies that have intense fluorescent properties and increased intensity of paramagnetic behavior are needed for practical applications.
Monolayer-protected thiolated gold nanoclusters are stable metal nanoparticles that are passivated by a layer of organic material. They have attracted much attention since their first description about 15 years ago due to their interesting physiochemical properties and their potential applications in bioimaging and theranostics. Most known syntheses of these gold nanoclusters result in products that have noble-gas-like superatomic electron configuration, such as Au25(SR)18− and Au102(SR)44. The gold nanoclusters that correspond to the closed-shell configuration are the results of thermodynamic stabilization. The synthesis of new gold nanoclusters with different molecular compositions should provide new and enhanced properties that could provide additional applications such as bioimaging and theranostics. Thus, there is a need for novel nanoclusters that display enhanced properties such as increased quantum yield of fluorescence and extended lifetime so that the nanoclusters offer better performance in these applications.